bursa-equivalent tissue (bursal equivalent tissue) a hypothesized lymphoid tissue in nonavian vertebrates including human beings, equivalent to the bursa of Fabricius in birds: the site of B lymphocyte maturation. It now appears that B lymphocyte maturation occurs primarily in the bone marrow.

cancellous tissue the spongy tissue of bone.

cartilaginous tissue the substance of cartilage.

chordal tissue the tissue of the notochord.

chromaffin tissue a tissue composed largely of chromaffin cells, well supplied with nerves and vessels; it occurs in the adrenal medulla and also forms the paraganglia of the body.

subcutaneous tissue the layer of loose connective tissue directly under the skin.

tissue typing identification of tissue types for purposes of predicting acceptance or rejection of grafts and transplants. The process and purposes of tissue typing are essentially the same as for blood typing. The major difference lies in the kinds of antigens being evaluated. The acceptance of allografts depends on the hla antigens (HLA); if the donor and recipient are not HLA identical, the allograft is rejected, sometimes within minutes. The HLA genes are located in the major histocompatibility complex, a region on the short arm of chromosome 6, and are involved in cell-cell interaction, immune response, organ transplantation, development of cancer, and susceptibility to disease. There are five genetic loci, designated HLA-A, HLA-B, HLA-C, HLA-D, and HLA-DR. At each locus, there can be any of several different alleles.

Each person inherits one chromosome 6 from the mother and one from the father; that is, each parent transmits to the child one allele for each kind of antigen (A, B, C, D, and DR). If the parents are different at both alleles of a locus, the statistical chance of one sibling being identical to another is one in four (25 per cent), the chance of being identical at one allele only (half-identical) is 50 per cent, and the chance of a total mismatch is 25 per cent.

Techniques for Tissue Typing. Histocompatibility testing involves several basic methods of assay for HLA differences. The most widely used method uses the polymerase chain reaction to compare the DNA of the person, organ, or graft being tested with known pieces of the genes encoding MHC antigens. The variability of these regions of the genes determines the tissue type of the subject.

Serologic methods are used to detect serologically defined antigens on the surfaces of cells. In general, HLA-A, -B, and -C determinants are primarily measured by serologic techniques. A second method, involving lymphocyte reactivity in a mixed lymphocyte culture, for determining HLA-D or lymphocyte-defined antigens, is now only rarely used.

Essentially, the serologic method is performed by incubating target lymphocytes (isolated from fresh peripheral blood) with antisera that recognize all known HLA antigens. The cells are spread in a tray with microscopic wells containing various kinds of antisera and are incubated for 30 minutes, followed by an additional 60-minute complement incubation. If the lymphocytes have on their surfaces antigens recognized by the antibodies in the antiserum, the lymphocytes are lysed. A dye is added to show changes in the permeability of the cell membrane and cellular death. The proportion of cells destroyed by lysis indicates the degree of histologic incompatibility. If, for example, the lymphocytes from a person being tested for HLA-A3 are destroyed in a well containing antisera for HLA-A3, the test is positive for this antigen group.

adipose tissue

areolar tissue

A form of loose connective tissue consisting of fibroblasts in a matrix of tissue fluid and collagen and elastin fibers. Many white blood cells are present. It is found subcutaneously and beneath the epithelium of all mucous membranes. See: connective tissue for illus

BONE TISSUE

bone tissue

bronchus-associated lymphoid tissue

Abbreviation: BALT

Lymph nodules that contain clusters of T and B lymphocytes and macrophages within the mucosa of the bronchial wall; a component of the mucosal immune system that defends all mucosal surfaces against pathogens.

chordal tissue

chromaffin tissue

cicatricial tissue

connective tissue

Tissue that supports and connects other tissues and parts of the body. Connective tissue has comparatively few cells. Its bulk consists of intercellular substance or matrix, whose nature gives each type of connective tissue its particular properties. The vascular supply varies: cartilage, none; fibrous, poor; adipose, good; and bone, abundant. Connective tissue includes the following types: areolar, adipose, fibrous, elastic, reticular, cartilage, and bone. Blood may also be considered a connective tissue.

illustration

elastic tissue

A form of connective tissue in which yellow elastic fibers predominate. It is found in certain ligaments, the walls of blood vessels, esp. the larger arteries, and around the alveoli of the lungs.

embryonic tissue

Any tissue that arises from the fertilization of an ovum and has not become differentiated or specialized.

epithelial tissue

erectile tissue

fatty tissue

fibrous tissue

Connective tissue consisting principally of collagen fibers. Also called white fibrous or dense connective tissue; may be regular (parallel fibers) or irregular.

gelatiginous tissue

Tissue from which gelatin may be obtained by treating it with hot water.

glandular tissue

A group of epithelial cells capable of producing secretions.

granulation tissue

The newly formed vascular and connective tissue produced in the early stages of wound healing.

hard tissue

In dentistry, the term used to denote any of the three calcified tissue components of the tooth: enamel, dentin, and cementum.

homologous tissues

Tissues that are identical in structure.

indifferent tissue

Tissue composed of undifferentiated cells as in embryonic tissue.

interstitial tissue

Connective tissue that forms a network with the cellular portions of an organ.

lymphadenoid tissue

Aggregates of lymphatic tissue found in the spleen and lymph nodes.

lymphoid tissue

Collections of lymphocytes in all stages of development found in the spleen, thymus, lymph nodes, lymph nodules of the digestive tract (tonsils, Peyer's patches), and the respiratory, urinary, and reproductive tracts.

mesenchymal tissue

The embryonic mesenchyme.

mucosa-associated lymphoid tissue

Abbreviation: MALT

Aggregates of T and B lymphocytes found in all mucous membranes, a line of defense against infection. Examples include Peyer's patches in the small intestine and lymph nodules in the colon, trachea, and bronchi. MALT contains CD4+ and CD8+ T cells and activated B cells and may occasionally undergo malignant transformation into lymphomas.

scar tissue

sclerous tissue

skeletal tissue

soft tissue

Any noncalcified tissue in the body. This term is especially used in relation to muscles, tendons, ligaments, skin, fat, and other connective tissues that are occasionally the source of pain when they are injured. Unlike bones or joints, which can be fractured or dislocated, soft tissues are bruised or inflamed by trauma. In surgery, soft tissues are dissected. By contrast, components of the (hard) bony skeleton are sawed, chiselled, or drilled. Soft tissues include all types of tissue except bone, i.e., all epithelial, muscle, and nerve tissue, as well as connective tissue excluding bone.

splenic tissue

The highly vascular splenic pulp.

subcutaneous tissue

fatty

organic compounds of carbon, hydrogen and oxygen that are esterified with glycerol to form fat. All fats are esters of fatty acids and glycerol, the fatty acids accounting for 90% of the molecule of most natural fats. A fatty acid consists of a long chain of carbon atoms with a carboxylic acid group at one end. Saturated fatty acids have no double bonds in the carbon chain. The medium and long chain fatty acids are solid at room temperature and are the components of the common animal fats, such as butter and lard. Unsaturated fatty acids contain one or more double bonds. The unsaturated fatty acids are liquid at room temperature and are found in oils such as olive oil and linseed oil. Polyunsaturated fatty acids have two or more double bonds.

Volatile fatty acids (VFAs) including acetic, butyric and propionic acids are produced in large quantities in the rumen by the fermentative digestion of cellulose. Much of the energy consumption of ruminants comes from these VFAs in the situation in which other animals use glucose. See also 3-omega fatty acid (below).

fatty acid nutritional deficiency

a secondary deficiency occurs in pigs on high-calcium diets. This may have a connection with parakeratosis of pigs caused by zinc deficiency and calcium excess in the diet. Requirements for dietary fat in dogs and cats are usually expressed as the essential linoleic acid and arachidonic acid.

fatty acid synthase

in bacteria, a multiprotein complex; in mammals, a single multifunctional protein important in the synthesis of palmitate as a major source of fatty acids.

fatty acyl CoA

generic term for long hydrocarbon chains, generally between C12 and C20, linked via thioester to coenzyme A.

fatty acyl CoA:cholesterol acyltransferase

enzyme (ACAT) catalyzing the transfer of fatty acyl group to cholesterol, irreversible physiologically. Its action regulates the number of LDL receptors by converting excess cholesterol (which inhibits LDL receptors) to cholesterol esters.

branched chain fatty acids

fatty acids usually containing a methyl branch; lowers the melting point compared with the equivalent straight chain fatty acid.

accumulation of fat in a liver beyond the level which is normally encountered may be a result of a normal physiological response to increased peripheral lipolysis, obesity or the action of hepatotoxins.

1. a disease of laying birds housed in battery cages. The cause is unknown. Affected birds are significantly heavier, there is a fall in egg production and they die acutely of liver rupture. The liver is greasy, mushy in consistency and yellow in color.

2. a severe fatty accumulation in the liver and hypertriglyceridemia that may develop in obese cats that are anorexic. There is jaundice, weight loss, neurological signs and a high mortality. Called also idiopathic feline hepatic lipidosis.

omega-3 (n-3) fatty acids

include α-linolenic acid, eicosapentanoic acid, docosahexanoic acid. High concentrations found in cold water marine (fish) oils.

omega-6 (n-6) fatty acids

found in terrestrial plants, including safflower oil, corn oil and evening primrose oil, which is a rich source of linoleic and arachidonic acids.

When the system is in use, a small needle--connected to a tube and inserted into the fatty tissue of the abdomen--measures the glucose level in the tissue every 10 seconds and sends a quantitatively proportionate electronic signal to a monitor to which it is connected.

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